Cellophane laminate utilized as dye imbibition receiving layer

ABSTRACT

DYE IMBIBITION COLOR REPRODUCTIONS EMPLOYING A DIMENSIONALLY STABLE CELLOPHANE LAMINATE.

United States Patent U.S. C]. 96-48 R 6 Claims ABSTRACT OF THE DISCLOSURE Dye imbibition color reproductions employing a dimensionally stable cellophane laminate.

DISCLOSURE OF THE INVENTION This invention relates to a process of producing multicolor reproductions by dye imbibition imaging using a dimensionally stable cellophane laminate as the receiving layer for each color.

Recently, a dye-imbibition pre-press color proofing system was introduced to the graphic arts, which permits a color separation house or color printer to produce accurate simultations of the final multi-color printing job prior to making printing plates. In this process, a paper sheet bearing a hydrophilic layer is sensitized by flowcoating 2. light-sensitive solution over the hydrophilic layer. The sensitized side of the paper sheet is placed in contact with a color separation transparency, exposed to actinic radiation, developed with dry powder containing a water soluble dye or dyes to embed the developing powder in the light-sensitive layer in image-wise configuration and treated with moist warm air (water vapor) to imbibe the dye or dyes from the dry powder into the hydrophilic layer in image-wise configuration. The sensitizer and developing powder remaining on the surface of the hydrophilic layer are removed with an appropriate solvent. The process is repeated for each color with each separation in register with the color or colors previously deposited.

In spite of its many advantages, this process has the disadvantage that the color balance of the proof and the printed job are dependent upon the coloration of the paper stock employed in each process. Typically, the hue in the tint areas is dependent on the color of the coated stock, which is due primarily to the human eye integrating an averaging the colors deposited in the half-tone tint areas and the paper color in the background areas. Even in the solid areas, where the background paper color is essentially masked, the human eye tends to pick up the paper color in the areas surrounding the solid areas, resulting in a somewhat distorted impression of the color or colors deposited in the solid areas. Since there are numerous stocks used in color printing processes, some interpretation of dye imbibition proofs is often necessary to compensate for the difference in paper stock used in the proofing process and the paper stock to be used in the printing operation.

Although hydrophilic dye imbibition receiving layers can be applied to paper stock by typical manual coating techniques, the hydrophilic layer should be applied to proofing stock under carefully controlled conditions, preferably by machine coating, to obtain optimum results in the instant proofing process. In elfect, this means that it is virtually impossible to provide a sufiicient number of coated stocks for use by all printers and/or color separation houses. Further, since color proofing is really a control method, reproducibility from proof to proof must be considerably greater than reproducibility from printed sheet to printed sheet. Accordingly, it is essential 3,687,666 Patented Aug. 29, 1972 that the hydrophilic layer on each sheet of profing stock has the same properties.

The hydrophilic receiving layer must be water swellable and have relatively good water resistance in order to accept 2, 3, 4 or more colors into the receiving layer Without any alteration of the properties of the hydrophilic layer. Due to the moistening and remoistening of the hydrophilic receiving layer during dye imbibition, it is usually necessary to cross-link the hydrophilic layer. Failure to cross-link most hydrophilic layers results in the hydrophilic surface becoming sticky after dye imbibition of the second, third or subsequent colors. In extreme cases, the selectivity of the sensitizer employed to produce the third and subsequent colors may be alfected by this stickness with the result that developing powder is embedded in non-image areas. In other cases, the dye or dyes may migrate or bleed from the point of powder embedment during dye imbibition yielding a somewhat fuzzy appearing proof. However, even when a suitably controlled concentration of cross-linking agent is added to the hydrophilic layer during machine coating, it often takes as long as thirty days for cross-linking to go to completion to insure a coated sheet having the necessary reproducible properties during proofing. Accordingly, for optimum results in color proofing, the coated hydrophilic layer must be applied to proofing stock under carefully controlled conditions and usually stored for some time in order to permit cross-linking or hardening of the hydrophilic layer to go to completion before the proofing stock is employed in the aforementioned proofing process.

As indicated above, the instant proofing process employs moist warm air to imbibe dye from the developing powder into the hydrophilic receiving layer. Since water is a plasticizer for both the paper stock and the hydrophilic receiving layer, care must be exercised in the proofing operation to assure that the proofing stock returns to essentially its same dimensions after each dye imbibition step. While the paper stock will return to essentially its same dimensions on equilibrating to ambient room conditions, an auxiliary heater is often employed to speed up the equilibration. If the proofing paper does not return to its same dimensions prior to resensitization and exposure, the final poof will contain areas that are out of register. Accordingly, it is desirable to employ a proofing stock which is not subject to dimensional changes during the dye imbibition steps.

The principal object of this invention is to provide a method of dye imbibition color proofing which is not dependent on variations in paper stock. Other objects will appear hereinafter.

I have now found that cellophane laminates comprising a dimensionally stable water-imprevious, preferably transparent, base and a cellophane layer laminated thereto, can be employed advantageously in the aforementioned process. The cellophane layer (regenerated cellulose layer) seems to be uniquely suited for use in this process in the sense that it is substantially water-insoluble without cross-linking and has the necessary properties to function as a dye imbibition receiving layer. Dye-imbibition color proofs made on cellophane laminates, can be placed over virtually any colored printing stock simulating almost exactly the final press run. When dye-imbibition proofs produced on paper proofing stock are compared with proofs made on cellophane laminates positioned over the same color paper proofing stock, the color balance of the two sets of proofs are virtually identical except for a very slight difference in intensity of the colors. Accordingly, dimensionally stable cellophane laminates are ideal for color proofing. If desired, these laminates can also be used advantageously to produce color projection slides.

In somewhat greater detail, multi-color reproductions are prepared in accordance with this invention by coating, preferably flow-coating a light-sensitive solution capable of developing 21 R of 0.9 to 2.2 over the dimensionally stable cellophane laminate, permitting the sensitizer solution to dry, placing the sensitized side of the cellophane laminate in contact with a first color separation transparency, exposing the element to actinic radiation to establish a potential R of 0.9 to 2.2, applying a dry powder contain'mg a water soluble dye or dyes to the exposed light-sensitive layer, embedding the developing powder in image-wise configuration into the light-sensitive layer, treating the light-sensitive element with moist warm air (water vapor) to imbibe the dye or dyes from the dry powder into the cellophane receiving layer in image-wise configuration. The sensitizer and developing powder remaining on the surface of the hydrophilic layer are removed with a solvent, exposing the original cellophane surface. The cellophane side of the laminate is resensitized and the process repeated for each of the color separations.

As pointed out above, the cellophane laminates employed in this invention are composed of a dimensionally stable transparent wateri-mpervious base and a cellophane dye imbibition receiving layer. Suitable transparent bases include polyesters (polyethylene terephthalate), cellulose esters (cellulose acetate, cellulose propionate, cellulose butyrate, etc.), polystyrene, polyethylene, polypropylene, etc. The transparent base may be laminated directly to the cellophane layer or a transparent subbing layer may be employed in order to enhance adhesion of the cellophane receiving layer to the base. These laminates can be prepared by typical coating technology, such as by passing the dimensionally stable water-impervious base through a cellulose xanthate bath and regenerating the cellophane on the surface of the dimensionally stable base. Alternatively, preformed cellophane layers can be laminated to the dimensionally stable base by techniques known to those skilled in the coating arts.

The light-sensitive layers are formed by applying a thin layer of solid, light-sensitive, film-forming organic material having a potential R of 0.9 to 2.2 to the cellophane layer by any suitable means dictated by the nature of the film-forming organic material and/ or the base (hotmelt, draw down, spray, roller coating or air knife, flow, dip or whirler coating, curtain coating, etc.) so as to produce a reasonably smooth, homogeneous layer of from 0.1 to 40 microns thick employing suitable solvents as necessary. Due to the nature of the equipment offered to the trade for use of the dye imbibition pre-press color proofing system described above, it is preferable that the light-sensitive layer be applied by flow-coating.

As indicated above, the light-sensitive elements employed in this invention have a R, of 0.9 to 2.2. If the R is below 0.9, the finished reproduction will lack the necessary tonal range. On the other hand, if the R is above 2.2, the developing powder will not embed as a monolayer and the light-sensitive layer may stick to the transparency in vacuum frame exposure equipment. The R of positiveacting, light-sensitive layers, which is called R is a photometric measurement of the reflection density of a black powder developed light-sensitive layer after a positive-acting, light-sensitive layer has been exposed to sufiicient actinic radiation to convert the exposed areas into substantially powder-non-receptive state (clear the background). The R of a negative-acting, light-sensitive layer, which is called R is a photometric measurement of the reflection density of a black powder developed area, after. a negative-acting, light-sensitive layer has been exposed to sufiicient actinic radiation to convert the exposed areas into a powder-receptive state.

The reflection density of a solid, positive-acting, lightsensitive layer (R is determined by coating the lightsensitive layer on a white substrate, exposing the light-sensitive layer to sufficient actinic radiation image-wise to clear the background of the solid, positive-acting, lightsensitive layer, applying a black powder (prepared from 77% Pliolite VTL and 23% Neo Spectra carbon black in the manner described below) to the exposed layer, physically embedding said black powder under the conditions of development as a monolayer in a stratum at the surface of said light-sensitive layer and removing the non-embedded particles from said light-sensitive layer. The de veloped organic layer containing black powder embedded image areas and substantially powder free-non-image areas is placed in a standard photometer having a scale reading from 0 to reflection of incident light or an equivalent density scale, such as on Model 500 A photometer of the Photovolt Corporation. The instrument is zeroed (0 density; 100% reflectance) on a powder free non-image area of the light-sensitive organic layer and an average R reading is determined from the powder developed area. The reflection density is a measure of the degree of blackness of the developed surface which is relatable to the concentration of particles per unit area. The reflection density of a solid, negative-acting, light-sensitive layer (Ran) is determined in the same manner except that the negative-acting, light-sensitive layer is exposed to sufficient actinic radiation to convert the exposed area into a powderreceptive area. If the R under the conditions of development is between 0.9 and 2.2, the solid, light-sensitive organic material deposited in a layer is suitable for use in this invention.

Although the R of light-sensitive layers is determined by using the aforesaid black developing powder and a white substrate, the R is only a measure of the suitability of a light-sensitive layer for use in the present invention.

Since the R of any light-sensitive layer is dependent on numerous factors other than the chemical constitution of the light-sensitive layer, the light-sensitive layer is best defined in terms of its R under the development conditions of intended use. The positive-acting, solid, lightsensitive organic layers useful in this invention must be powder receptive in the sence that the aforesaid black developing powder can be embedded as a monoparticle layer into a stratum at the surface of the unexeposed layer to yield a R of 0.9 to 2.2 (1.0 to 2.0 preferably) under the predetermined conditions of development and lightsensitive in the sense that upon exposure to actinic radiation the most exposed areas can be converted into the nonparticle receptive state (background cleared) under the predetermined conditions of development. In other words, the positive-acting, light-sensitive layer must contain a certain inherent powder receptivity and light-sensitivity. The positive-acting, light-sensitive layers are apparently converted into the poWder-non-receptive state by a light catalyzed hardening action, such as photopolymerization, photocrosslinking, photooxidation, etc. Some of these photohardening reactions are dependent on the presence of oxygen, such as the photooxidation of internally ethylenically unsaturated acids and esters while others are inhibited by the presence of oxygen, such as those based on the photopolymerization of vinylidene or polyvinylidene monomers alone or'together with polymeric materials. The latter requires special precautions, such as storage in oxygen-free atmosphere or oxygen-impermeable cover sheets. For this reason, it is preferably to use solid, positive-acting, film-forming, organic materials containing no terminal ethylenic unsaturation.

The negative-acting, solid, light-sensitive organic layers useful in this invention must be light-sensitive in the sense that, upon exposure to actinic radiation, the most exposed areas of the light-sensitive layer are converted from a nonpoWder-receptive state under the predetermined conditions of development to a powder-receptive state under the predetermined conditions of development. In other words, the negative-acting, light-sensitive layer must have a certain minimum light-sensitivity and potential powder receptivity. The negative-acting, light-sensitive layers are apparently converted into the powder-receptive state by a light-catalyzed softening action, such as photodepolymerization, photoisomerization, etc.

In general, the positive-acting, solid, light-sensitive layers useful in this invention comprises, a film-forming organic material in its naturally occurring or manufactured form or a mixture of said organic material with plasticizers and/or photoactivators for adjusting powder receptivity and sensitivity to actinic radiation. Suitable positive-acting, film-forming organic materials, which are not inhibited by oxygen, include internally ethylenically unsaturated acids, such as abietic acid, rosin acids, partially hydrogenated rosin acids, such as those sold under the name Staybelite resin, wood rosin, etc., esters of internally ethylenically unsaturated acids, methylol amides of maleated oils such as described in US. Pat. 3,471,466, phosphatides of the class described in application Ser. No. 796,841, filed on 'Feb. 5, 1969, now US. Pat. 3,585,031, in the name of Hayes, such as soybean lecithin, partially hydrogenated lecithin, dilinolenyl alpha lecithin, etc., partially hydrogenated rosin acid esters, such as those sold under the name Staybelite esters, rosin modified alkyds, etc.; polymers of ethylenically unsaturated monomers, such as vinyltoluene-alpha methyl styrene copolymers, polyvinyl cinnamate, polyethyl methacrylate, vinyl acetatevinyl stearate copolymers, polyvinyl pyrrolidone, etc.; coal tar resins such as cournarone-indene resins, etc.; halogenated hydrocarbons, such as chlorinated waxes, chlorinated polyethylene, etc. Positive-acting, light-sensitive materials, which are inhibited by oxygen include mitxures of polymers, such as polyethylene terephthalate/sebacate, or cellulose acetate or acetate/butyrate, with polyunsaturated vinylidene monomers, such as ethylene glycol diacrylate or dimethacrylate, tetraethylene glycol diacrylate or dimethacrylate, etc.

Although numerous positive acting, film forming organic materials have the requisite light-sensitivity and powder-receptivity at predetermined development temperatures, it is generally preferable to compound the filmforming organic material with photoactivator(s) and/or plasticizer(s) to impart optium powder receptivity and light-sensitivity to the light-sensitive layer. In most cases, the light-sensitivity of an element can be increased many told by incorporation of a suitable photoactivator capable of producing free-radicals, which catalyze the light-sensitive reaction and reduce the amount of photons necessary to yield the desired physical change.

Suitable photoactivators capable of producing free-radicals include benzil, benzoin, Michlers ketone, diacetyl, phenanthraquinone, p-dimethylaminobenzoin, 7,8-benzofia-vone, trinitrofiuorenone, desoxybenzoin, 2,3-pentanedione, dibenzylketone, nitroisatin, di(6-dimethylamino-3- pyradil)methane, metal napthanates, N-methyl-N-phenylbenzylamine, pyridil, 5,7 dichloroisatin, azodiisobutyronitrile, trinitroanisole, chlorophyll, isatin, bromoisatin, etc. These compounds can be used in a concentration of .001 to 2 times the weight of the film-forming organic material .1%200% the weight of film former). As in most catalytic systems, the best photoactivator and optimum concentration thereof is dependent upon the film-forming organic material. Some photoactivators respond better with one type of film former and may be useful with substantially all film-formers in wide concentration ranges.

The acyloin and vicinal diketone photoactivators, particularly benzil and benzoin are preferred. Benzoin and benzil are effective over wide concentration ranges with substantially all film-forming, light-sensitive organic materials. Benzoin and benzil have the additional advantage that they have a plasticizing or softening effect on filmforming, light-sensitive layers, thereby increasing the powder receptivity of the light-sensitive layers. When employed as a photoactivator, benzil should preferably comprise at least 1% by weight of the film-forming organic material (.01 times the film former weight).

Dyes, optical brighteners and light absorbers can be used alone or preferably in conjunction with the aforesaid free-radical producing photoactivators (primary photoactivators) to increase the light-sensitivity of the lightsensitive layers of this invention by converting light rays into light rays of longer lengths. For convenience, these secondary photoactivators (dyes, optical brighteners and light absorbers) are called superphotoactivators. Suitable dyes, optical brighteners and light absorbers include 4 methyl-7-dimethylaminocoumarin, Calcofiuor yellow HEB (preparation described in U.S. Pat. 2,415,373), Calcofluor white SB super 30080, Calcofluor, Uvitex W conc., Uvitex TXS conc., Uvitex RS (described in Textil-Rundschau 8 [1953], 339), Uvitex WGS conc., U-vitex K, Uvitex CF conc., Uvitex W ,(described in Textil-Rundschau 8 [1953], 340), Aclarat 8678, Clancophoe OS, Tenopol UNPL, MDAC S8844, Uvinul 400, Thilfiavin TGN conc., Aniline yellow-S (low conc.), Seto flavine T 5506440, Auramine O, Calcozine yellow OX, Calcofluor RW, Calcofluor GAC, Acetosol yellow 2 RLS-PHF, Eosine bluish, Chinoline yellow-P conc., Ceniline yellow S (high conc.), Anthracene blue Violet fluorescence, Calcofiuor white MR, Tenopol PCR, Uvitex GS, Acid-yellow-T-supra, Acetosol yellow 5 GLS, Calcocid OR. Y. Ex. Conc., diphenyl brilliant fiavine 7 GF'F, Resoflorm fluorescent yellow 3 GPI, Eosin yellowish, Thiazole fiuorescor G, Pyrazalone orange YB-3, and National FD&C yellow. Individual superphotoactivators may respond better with one type of light-sensitive organic film-former and photoactivator than with others. Further, some photoactivators function better with certain classes of brighteners, dyes and light absorbers. For the most part, the most advantageous combinations of these materials and proportions can be determined by simple experimentation.

As indicated above, plasticizers can be used to impart optimum powder receptivity to the light-sensitive layer. With the exception of lecithin, most of the film-forming, light-sensitive organic materials useful in this invention are not powder-receptive at room temperature but are powder-receptive above room temperature. Accordingly, it is desirable to add sufiicient plasticizer to impart room temperature (15 to 30 C.) or ambient temperature powder-receptivity to the light-sensitive layers and/or increase the R range of the light-sensitive layers to at least 0.9.

While various softening agents, such as dimethyl siloxanes, dimethyl phthalate, glycerol, vegetable oils, etc. can be used as plasticizers, benzil and benzoin are preferred since, as pointed out above, these materials have the additional advantage that they increase the lightsensitivity of the film-forming organic material. As plasticizer-photoactivators, benzoin and benzil are preferably used in a concentration of 1% to by weight of the film-forming solid organic material.

The preferred positive-acting, light-sensitive film formers containing no conjugated terminal ethylenic unsaturation include the esters and acids of internally ethylenically unsaturated acids, particularly the phosphatides, rosin acids, partially hydrogenated rosin acids and the partially hydrogenated rosin esters. These materials, when com pounded with suitable photoactivators, preferably acyloins or vicinal diketones together with superphotoactivators, require less than 2 minutes exposure to clear the background of light-sensitive layers.

In general, the negative-acting, light-sensitive layers useful in this invention comprise a film-forming organic material in its naturally occurring or manufactured form, or a mixture of said organic material with plasticizers and/or photoactivators for adjusting powder receptivity and sensitivity to actinic radiation. Suitable negativeacting, film-forming organic materials include n-benzyl linoleamide, dilinoleyl-alpha-lecithin, castor wax (glycerol 12-hydroxy-stearate), ethylene glycol monohydroxy stearate, polyisobutylene, polyvinyl stearate, etc. Of these, castor wax and other hydrogenated ricinoleic acid esters (hydroxystearate) are preferred. These materials can be compounded with plasticizers and/or photoactivators in the same manner as the positive-acting, light-sensitive, film-forming organic materials.

Some solid, light-sensitive organic film formers can be used to prepare either positive or negative-acting, lightsensitive layers. For example, a poly(n-butyl methacrylate) layer containing 20 percent benzoin (20 parts by weight benzoin per 100 parts by Weight polymer) yields good positive-acting images. Increasing the benzoin level to 100 percent converts the poly(n-butyl methacrylate) layer into a good negative-acting system.

The light-sensitive layer must be at least 0.1 micron thick and preferably at least 0.4 micron in order to hold suitable powders during development. If the light-sensitive layer is less than 0.1 micron, or the developing powder diameter is more than 25 times layer thickness, the light-sensitive layer does not hold the developing powder with the necessary tenacity. In general, as layer thickness increases, the light-sensitive layer is capable of holding larger particles. However, as the light-sensitive layer thickness increases, it becomes increasingly difficult to maintain film integrity during film development. Accordingly, the light-sensitive layer must be from 0.1 to 40 microns, preferably from 0.4 to 2.5 microns.

The preferred method of applying light-sensitive layers of predetermined thicknesses to the cellulose side of the laminate comprises flow-coating a solution in an organic solvent vehicle (hydrocarbons, such as hexane, heptane, benzene, etc.; halogenated hydrocarbons, such as chloroform, carbon tetrachloride, 1,1,l-trichloroethane, trichloroethylene, etc.; alcohols, such as ethanol, methanol, isopropanol, etc.; ketones, such as acetone, methyl ethyl ketone, etc.) of the light-sensitive organic film-former alone or together with dissolved or suspended photoactivators or plasticizers onto the base. The hydrocarbons and halo'hydrocarbons, which are excellent solvents for the preferred positive-acting, light-sensitive film formers, containing no terminal conjugated ethylenic unsaturation, are the preferred vehicles because of their high volatility and low cost. Typically, solutions prepared with these vehicles can be applied to the base and air dried to a continuous clear film in less than one minute. In general, the halohydrocarbons have the advantage that they are non-flammable and can be used without danger of flash fires. However, many of these, such as chloroform and carbon tetrachloride must be handled with care due to the toxicity of their vapors. Of all these solvents, 1,1,1-trichloroethane is preferred since it has low toxicity, is non-flammable, low cost and has high volatility. In general, the thickness ofthe lightsensitive layer can be varied as a function of the concentration of the solids dissolved in the solvent vehicle.

After the base is coated with a suitable solid, lightsensitive organic layer, a latent image is formed by exposing the element to actinic radiation in image-receiving manner for a time sufiicient to provide a potential R of 0.9 to 2.2 (clear the background of the positive-acting, light-sensitive layers or establish a potential R of 0.9 to 2.2 with negative-acting, light-sensitive layers). The light-sensitive elements can be exposed to actinic radiation through a photographic positive or negative, which may be line, half-tone or continuous tone.

As indicated above, the latent images are preferably produced from positive-acting, light-sensitive layers by exposing the element in image-receiving manner for a time sufficient to clear the background, i.e. renderthe exposed areas non-powder-receptive. As explained in commonly assigned application Ser. No. 796,847, now US. Pat. 3,637,385, the amount of actinic radiation necessary to clear the background varies to some extent with, developer powder size and development conditions. Dueto these variations it is often desirable to slightly overexpose line and half-tone images in order to assure com plete clearing of the background. Slightly more care is necessary in producing continuous-tone powder images since overexposure tends to decrease the tonal range of the developed image. In general, overexposure is preferred with negative-acting, light-sensitive elements in order to provide maximum contrast.

After the light-sensitive element is exposed to actinic radiation for a time sufiicient to clear the background of a positive-acting, light-sensitive layer or establish a potential R of 0.9 to 2.2, a developing powder having a diameter or dimension along one axis of at least 0.3 micron comprising a solid carrier and a dye is applied physically with a suitable force, preferably mechanically, to embed the powder in the light-sensitive layer. The developing powder can be virtually any shape, such as spherical, acicular, platelets, etc.

The developing powders suitable for use in dye imbibition imaging processes comprise one or more watersoluble dyes and preferably a solid carrier. The solid carrier is preferably used in order to control particle size of the developing powders and to control the intensity of the final dye image. The dye or dyes can be ball-milled with the solid carrier in order to coat the carrier with dye. If desired, dyes can be blended above the melting point with various solid carriers, ground to suitable size and classified. In some cases it is advantageous to dissolve dye and carrier in a mutual solvent, dry and grind to suitable size. Preferably, the carrier is coated with dye, since the dye is more readily and more efficiently imbibed into the substrate. If the dye is in the carrier matrix, more dye must be employed to obtain comparable brilliance and image density. However, the latter route tends to preelude individual dye particles from embedding in nonimage areas.

Suitable solid carriers include polymeric or resinous materials, such as Pliolite VTL (vinyltoluene-butadiene copolymer), polymethyl methacrylate, polystyrene, rice starch, corn starch, phenol-formaldehyde resins, etc.; organic monomeric compounds such as hydroquinone, sorbitol, mannitol, dextrose, tartaric acid, urea, animal glue gelatin, gum arabic, carbowaxes, polyvinyl pyrrolidone, etc.; metal oxides and salts, such as titanium dioxide, magnesium oxide, zinc oxide, lead carbonate, calcium carbonate, barium sulfate, etc. Suitable metal powders include aluminum flakes, nickel flakes, rhodium powders, etc.

Suitable water soluble dyes include Alphazurine 2G, Calcocid Phloxine 2G, Tartrazine, Acid Chrome blue 3BA Conc., Acid Magenta 0., Ex. Conc., Neptune Blue BRA Conc., Nigrosine, Jet Cone, Patent Blue AF, Ex. Conc., Pontacyl Light Red 4BL Cone. 175%, etc.

For use in this invention, it is generally preferred that the solid carrier be water insoluble and 1,1,l-trichloroethane soluble. In this way, none of the solid carrier migrates into the cellpohane receiving layer during the dye imbibition step and the solid carrier can subsequently be removed readily with l,l,l-trichloroethane solution to restore the original characteristics of the cellophane receiving layerfor the next image.

. The black developing powder for determining the R of a light-sensitive layer is formed by heating about 77% Pliolite 'VTL (vinyltoluene-butadiene copolymer) and I 23 %'-Neo Spectra carbon black at a temperature above themelting point of the resinous carrier, blending on a rubber mill for fifteen minutes and then grinding in a Mikro-atomizer.

The developing powders useful in this invention contain. particles having a diameter or dimension along at least one axis from 0.3'to 40 microns, preferably from 0.5 to 10 microns with powders of the order of 1 to 15 microns being best" for light-sensitive layers of 0.4 to 10 microns. Maximum particle size is dependent on the thickness of light-sensitive layer while minimum particle size is independent of layer thickness. Electron microscope studies have shown that developing powders having a diameter 25 times the thickness of the light-sensitive layer cannot be permanently embedded into light-sensitive layers, and generally speaking, best results are obtained where the diameter of the powder particle is less than about times the thickness of the light-sensitive layer For the most part, particles over 40 microns are not detrimental to image development provided the developing powder contains a reasonable concentration of powder particles under 40 microns, which are less than 25 t1mes, and preferably less than 10 times, the light-sensitive layer thickness. However, other things being equal, the larger the developer powder particles (above 10 microns), the lower the R of the developed image.

Although particles over 40 microns are not detrimental to image development, the presence of particles under 0.3 micron diameter along all axes can be detrimental to proper image formation. In general, it is preferable to employ developing powders having substantially all powders having a diameter along at least one axis not less than 0.3 micron, preferably more than 0.5 micron, since particles less than 0.3 micron tend to embed in non-image areas. As the particle size of the smallest powder in the developer increases, less exposure to actinic radiation is required to clear the background.

In general, somewhat more deposition of powder particles into non-image areas can be tolerated when using a black developing powder than a colored powder, since the human eye is less offended by gray background in non-image areas than by the deposition of colored particles in non-image areas. Therefore, the concentration of particles under 0.3 micron and the size of the developing powder is more critical when using a cyan, magenta or yellow developing powder. For best results, the developing powder should have substantially all particles (at least 95% by weight) over 1 micron in diameter along one axis and preferably from 1 to microns for use with light-sensitive layers of from 0.4 to 10 microns. In this way, powder embedment in image areas is maximum and relatively little powder is embedded into non-image areas.

In somewhat greater detail, the developing powder is applied directly to the light-sensitive layer, while the powder receptive areas of said layer are in at most only a slightly soft deformable condition and said layer is at a temperature below the melting point of the layer and powder. The powder is distributed over the area to be developed and physically embedded into the stratum at the surface of the light-sensitive layer, preferably mechanically by force having a lateral component, such as to-and-fro and/or circular rubbing or scrubbing action using a soft pad or fine brush. If desired, the powder may be applied separately or contained in the pad or brush. The quantity of powder is not critical provided there is an excess available beyond that required for full development of the area, as the development seems to depend primarily on particle-to-particle interaction rather than brush-to-surface or pad-to-surface forces to embed a layer of powder particles substantially one particle thick (monoparticle layer) into a stratum at the surface of the lightsensitive layer. When viewed under an inverse microscope, spherical powder particles under about 10 microns in diameter enter the powder-receptive areas first and stop dead, embedded substantially as a monolayer. The larger particles seem to travel over the embedded smaller particles which do not rotate or move as a pad or brush is moved back and forth over the developed area. Nonspherical particles, such as platelets, develop like the spherical powders except that the flat side tends to embed. Only a single stratum of powder particles penetrates into the powder-receptive areas of the light-sensitive layer even if the light-sensitive layer is several times thicker than the developer particle diameter.

After the powder application, excess powder remains on the surface which has not been sufiiciently embedded into, or attached to, the film. This may be removed in any convenient way, as by wiping with a clean pad or brush usually using somewhat more force than employed in 10 mechanical development, by vacuum, by vibrating, or by air doctoring. For simplicity and uniformity of results, the excess powder is usually blown off using an air gun having an air line pressure of about 20 to 40 p.s.i.

After the non-embedded powder particles are removed from the surface of the light-sensitive layer, the embedded powder particles are separated from the cellophane receiving layer by the light-sensitive layer. The powder particles comprising a water soluble dye, held in imagewise configuration in particulate form in the light-sensitive layer, are contacted with water vapor, molecularly imbiding and transporting said dye into the cellophane receiving layer. Other things being equal, the particulate dye image changes from a pale or pastel color to a brilliant saturated, more pleasing hue. The light-sensitive layer, which preferably contains no conjugated terminal ethylenic unsaturation, is then removed from the surface of the cellophane with a solvent for the light-sensitive layer which is a poor solvent for the surface of the substrate. 1,1,1-trichloroethane is particularly well suited for use in this step. Removal of the light-sensitive layer and the carrier for the developing powder renews the surface of the cellophane layer so that it can be resensitized without the formation of minute hills and valleys associated with the normal embedded particles.

As indicated above, the water soluble dye is transported through the solid, organic layer. Although the transportation of the dye through the solid, organic layer is not completely understood, it is believed that in most cases dye imbibition is due to weakening of the light-sensitive layer by the powder particles employed during deformation imaging creating points of stress in the film surface. Subsequently, when water vapor, capable of swelling the surface of the cellophane upon which the stressed film is disposed, contacts the surface of the substrate, a second stress is placed upon the light-sensitive layer due to the swelling of the cellophane receiving layer with the result that the light-sensitive layer fractures and the dye is transported through the light-sensitive layer and imbided into the surface of the substrate. In other cases dye imbibition may be due to the water vapor diffusing the dissolved dye into the light-sensitive layer. In any event, the water vapor must be capable of transporting the dye through the light-sensitive layer Experiments have shown that the development of various light-sensitive elements, such as Staybelite Ester #10 and Staybelite resins, with developing powder weakens the film layer. For example, when these light-sensitive elements are developed with undyed developing powder, it is possible to imbibe water soluble dye into the receiving layer in image-wise configuration by merely dipping the developed light-sensitive element into an aqueous dye bath. In such case the water soluble dye enters the hydrophilic receiving layer in the areas defined by the undyed powder particles. Accordingly, in such case, it is clear that the transportation of the dye through the light-sensitive layer is at least partially due to weakening of the light-sensitive layer by developer particle.

It has also been found that the above light-sensitive materials have a tendency to puddle up in the exposed areas in image-wise configuration when merely exposed to light and treated with water vapors. Accordingly, dye imbibition of water-soluble dyes through these materials is also partially due to the ability of moist warm air to disrupt the unexposed areas of the light-sensitive layer. In other cases, such as in the case of phosphatide lightsensitive elements, the exposed areas of the light-sensitive layer are converted into a more water-soluble condition than the unexposed areas as explained in aforementioned copending application, Ser. No. 796,841 of Hayes, filed Feb. 5, 1969, now US. Pat. 3,585,301. In such case, water vapor tends to transport the dye image through the exposed areas of the light-sensitive element with the result that the original positive powder image changes into a negative dye imbibition image. In still other cases, it

1 1 has been possible to prevent passage of water-soluble dye into the dye imbibition receiving layer by adding various hydrophobic agents, such as silicone oils in a concentration of 200 parts per million to various light-sensitive layers, such as those based on Staybelite resins and esters. The silicone tends to act as a waterproofing agent in this environment and no dye imbibition with water vapor is possible since water vapor is incapble of transporting the dye through the light sensitive layer. Dye imbibition of water-soluble dye through light-sensitive layers based on poly(n-butyl methacrylate) and other high molecular weight hydrophobic polymers, is relatively difiicult due to the extreme hydrophobic nature of these film formers.

The preferred method of forming multi-color reproductions comprises coating the hydrophilic surface of the cellophane laminate with a halohydrocarbon solution of a light-sensitive organic film former containing no conjugated terminal ethylenic unsaturation to form a lightsensitive layer of from about 0.5 to 2.5 microns capable of developing a R, of 0.9 to 2.0; exposing said lightsensitive organic layer to actinic radiation in image-receiving manner to establish a potential R of 0.9 to 2.0; applying to said layer of organic material, free-flowing powder particles comprising a water soluble dye and a 1,1,1-trichloroethane soluble carrier, said powder particles having a diameter along at least one axis of at least one micron; while the element is at a temperature below the melting point of the powder and the organic layer, physically embedding said powder particles as a monolayer in a stratum at the surface of said light-sensitive layer to yield an image having portions varying in density in proportion to the exposure of each portion; removing non-embedded particles from said organic layer to develop an image; molecularly imbibing water-soluble dye into the cellophane substrate by contacting the particles embedded in said organic layer with vapors of water or steam; removing said light-sensitive organic film former containing no conjugated terminal ethylenic unsaturation and the carrier for said dye with 1,1,l-trichloroethane clearing agent; coating the substrate bearing the first color in image-wise configuration in the surface of said substrate with a solid, light-sensitive organic film former containing no conjugated terminal ethylenic nnsaturation, from a l,l,l-trichloroethane vehicle to form a second light-sensitive organic layer of from about 0.5 to 2.5 microns capable of developing a R of 0.9 to 2.0; exposing said light-sensitive layer to actinic radiation in image-receiving manner to establish a potential R of 0.2 to 2.0; applying to said layer of organic material free-flowing powder particles comprising a second water soluble dye and carrier, said powder particles having a diameter along one axis of at least one micron; while the layer is at a temperature below the melting points of the powder and of the organic layer, physically embedding said powder particles as a monolayer in a stratum at the surface of said second light-sensitive layer to yield an image having portions varying in density in proportion to the exposure of each portion; removing the nonembedded particles from said organic layer to develop a two color reproduction; molecularly imbibing water soluble dye into the cellophane substrate by contacting the particles embedded in said organic layer with vapors of water or steam; removing said second light-sensitive layer and second developing powder carrier with 1,1,1-trichloroethane clearing solution and repeating the process to form a third, fourth, fifth, etc. colored.

Reproductions formed using the above-described dimensionally stable cellophane laminates, can be used in the aforementioned color proofing process and/or in the production of slides.

The following examples are merely illustrative and should not be construed as limiting the scope of my invention.

12 EXAMPLE 1 Ninety-six hundredths of a gram of Staybelite Ester No. 10 (partially hydrogenated rosin ester of glycerol), .24 gram benzil and .14 gram 4-methyl-7-dimethylaminocoumarin, dissolved in mls. 1,1,l-trichloroethane was applied to the cellophane side of a cellophane-polyethylene terephthalate laminate by flow-coating the solution over the substrate supported at about a 60 angle with the horizontal. After air drying for approximately one minute, the light-sensitive layer was approximately one micron thick. The light-sensitive element was placed in a vacuum frame in contact with a yellow half-tone separation positive transparency and exposed to a mercury point light source for about 60 seconds. The light-sensitive element was removed from the vacuum frame and developed with a yellow developing powder composed of a Pliolite VTL carrier and Tartrazine dye of from about 1 to 40 microns diameter along the largest axis prepared in the manner described below. The yellow developing powder was embedded into the unexposed areas of the light-sensitive layer by rubbing a cotton pad containing the yellow developing powder back and forth over the light-sensitive layer using essentially the same force used in ultrafine finishing of wood surfaces by sanding or steel wooling. The excess powder was removed from the light-sensitive layer by impinging air at an angle of about 30 and wiping the reproduction with a fresh cotton pad resulting in an excellent half-tone reproduction of the positive transparency. The Tartrazine dye was molecularly dispersed and imbibed into the cellophane layer by moving a wand generating steam across the face of the light-sensitive layer. The molecularly dispersed image changed from a pale yellow to a brilliant, saturated, aesthetically more pleasing yellow hue. The light-sensitive layer and Pliolite VTL carrier were removed by flushing with l,l,l-trichloroethane.

After the image dried, the cellophane side of the laminate was resensitized with the same light-sensitive composition, placed in register with the magenta half-tone transparency, exposed for about 60 seconds, developed with a magenta developing powder comprising a Pliolite VTL carrier and a Calcocid Phloxine developing powder of from about 1 to 40 micron diameter along the largest axis (prepared in the manner described below); excess developing powder was removed in the manner described above and the magenta dye molecularly imbibed in image-wise configuration into the cellophane layer using moist warm air. The molecularly dispersed image changed from a pale magenta to a brilliant, saturated, aesthetically more pleasing magenta hue. The light-sensitive layer and carrier were removed by flushing with 1,1,1-trichloroethane.

The yellow/ magenta imaged sheet was recoated with the same sensitizer solution, air dried, placed in register with the half-tone cyan separation positive, exposed to light in the manner described above and developed with a cyan developing powder comprising a Pliolite VTL and a Neptune Blue developing powder of from about 1 to 40 microns in the manner described above. After the excess developing powder was removed, the cyan dye was molecularly dispersed and imbibed into the cellophane layer. The light-sensitive layer was washed with 1,1,l-trichl0roethane to remove the light-sensitive layer and carrier.

The three-color sheet was coated with the sensitizing solution and processed in the manner described above using a black half-tone separation transparency and a black developing powder composed of Pliolite VTL and Nigrosine WS dye of from about 1 to 40 microns diameter along the largest axis. After the excess powder was removed from the light-sensitive layer, the black dye Was molecularly dispersed in the cellophane layer in the manner described above. The light-sensitive layer and Pliolite VTL carrier were removed by flushing with l,l,l-trichloroethane.

When the above four-color proof on polyester-cellophane laminate was placed over a high-white sheet of 13 gelatin coated proofing stock and compared with a fourcolor proof produced in the same manner using another sheet of high-white gelatin coated stock, the proofs were essentially identical except that the cellophane laminate proof was slightly lower in intensity.

Essentially the same results are obtained by replacing each of the light-sensitive Staybelite Ester #10 compositions (partially hydrogenated rosin ester of glycerol) with (a) 1.25 grams Staybelite Ester (partially hydrogenated rosin ester of glycerol), .1875 gram benzil and .3125 gram 4-methyl-7-dimethylaminocoumarin, dissolved in 100 mls. 1,1,1-trichloroethane; (b) 1.25 grams Staybelite Resin F (partially hydrogenated rosin acids), .1 gram benzil and .3125 gram 4-methyl-7-dimethylaminocoumarin, dissolved in 100 mls. 1,1,l-trichlorocthane; (c)

1.25 grams wood rosin, .15 gram benzil and .3125 4- methyl-7-diethylaminocourmarin dissolved in 100 mls. 1,1,1-trichloroethane; (d) 1.25 grams abietic acid, .15 gram benzil and .3125 4-methyl-7-dimethylaminocoumarin, dissolved in 100 mls. 1,1,l-trichloroethane; and (e) 1.25 grams Chlorowax 70 LMP, .3 gram benzil and .3125 4-methyl-7-dimethylaminocoumarin, dissolved in 100 mls. 1,1,1-trichloroethane.

The developing powders employed in this example were prepared by milling the indicated number of grams of micronized Pliolite VTL and dye on a ball mill with porcelain balls for 12 hours: (1) 188 grams Pliolite VTL and 12 grams T artrazine; (2) 194 grams Pliolite VTL and 6 grams Caloocid Phloxine 2G; (3) 194 grams Pliolite VTL and 6 grams Neptune Blue; and (4) 176 grams Pliolite VTL and 24 grams Nigrosine WS.

EXAMPLE II A slide suitable for use in projection imaging can be prepared in the manner described above by employing continuous-tone separation positives in place of the halftone separation positives and by doubling the concentration of dye in each of the developing powders.

Since many embodiments of this invention may be made and since many changes may be made in the embodiments described, the foregoing is to be interpreted as illustrative only and my invention is defined by the claims appended hereafter.

What is claimed is:

1. The process of forming dye imbibition color reproductions comprising the steps of (l) coating the surface of a dimensionally stable cellophane laminate with a light-sensitive solution to form a solid, organic layer capable of developing a R of 0.9 to 2.2;

(2) exposing the element to actinic radiation to establish a potential R of 0.9 to 2.2;

(3) applying a dry powder comprising a water-soluble dye having a particle size of at least 0.3 micron in diameter along the largest axis to the exposed lightsensitive layer;

(4) embedding the developing powder in image-wise configuration into the light-sensitive layer while maintaining the light-sensitive layer below the melting point of the light-sensitive layer and the developing powder; and

(5) treating the light-sensitive element with moist warm air to transport said dye through said solid, organic layer, molecularly imbibing said dye in the dry powder into the cellophane receiving layer in image-wise configuration.

2. The process of claim 1, wherein said dimensionally stable cellophane laminate is a polyester-cellophane laminate.

3. The process of claim 1, wherein said light-sensitive soltuion is flow coated from a 1,1,1-trichloroethane solution.

4. The process of claim 3, wherein said light-sensitive composition is positive-acting.

5. The process of claim 4, wherein said developing powder comprises a carrier which is soluble in 1,1,1-trichloroethane.

6. The process of claim 5, wherein the light-sensitive layer and carrier portion of said developing powder is removed from the cellophane laminate after the dye imbibition step by flushing with 1,1,1-trichloroethane.

References Cited UNITED STATES PATENTS 12/1953 Miller et a1 117-34 12/1968 Coenen 96-48 R US. Cl. X.R. 

